Unseen
by LittleFireOfLife
Summary: Rin was diagnosed with a terminal disease at a young age. So when he discovered that he's the son of Satan, everything spiralled out of control. With Rin trying to keep his failing health a secret to his fellow exwires, and Amaimon sudden interest on him, Rin knew that everything is either going to get better or get worse. SLOW UPDATES
1. Chapter 1

It started when he was eight.

Shiro had sent Yukio home early to rest. He was talking to his teacher after he beat up the kid who's bullying Yukio earlier, when suddenly he felt something warm dripping from his nostrils.

"Huh?"

Rin touched his nostrils and found blood staining his fingers. From what he remembered, he didn't get punched on the nose or anything.

He looked at Shiro and opened his mouth to call him but his stomach had other plans.

Disgusting fluid came out of his mouth before he can stop it. He can barely heard Shiro calling out his name as his legs gave out and he quickly put his hands in front of him to stop himself from face planting into his vomit. His stomach did another round and fluid came out from his mouth again. But this time, it's not just vomit, there's red in it too.

 _'Blood,'_ Rin thought, _' I'm_ _vomiting blood.'_

A dizzy spell hit him like a ton of bricks. Black spots invaded his vision as he tried to stay concious. He can barely hear the sound of sirens at the distance.

His arms gave out beneath him. But before he collides with his vomit, warm hands stopped him and he knew no more.

UNSEEN=

As the doctor came out of the room, dread settled into Shiro's gut. The expression of the doctor is not a good one. 'What's wrong with Rin that made the doctor look like he's about to deliver the date of an execution?' Shiro thought

"The guardian of Okumura Rin?" The doctor is at his 30's, with messy short brown hair like he repeatedly ran his hand through it. He looked so stressed and sympathetic that Shiro's stomach did back flips.

"I'm sorry," the doctor sounds so regretful that Shiro wants to throw up. "Rin...have a terminal disease."

A lump formed in Shiro's throat. Tears stung his eyes but he blinked them away before they can escape.

"W-what?" Shiro managed to choke out.

The doctor ran his hand through his hair. "We found signs of terminal disease on Rin's blood. The disease is unknown. So we can't give him treatments. All we know is that it's slowly breaking down his organs inside out."

Shiro inhaled sharply, he wanted to curl up on a corner and cry his heart out. He half listened to the doctor as he said Rin have at least eight to ten years to live if he's lucky and he takes the medicine prescribed that will slow the illness down.

As the doctor finished talking about where he can buy the medicine and how many doses to give Rin. He put his hand on Shiro's shoulder and said,

"Be strong, for Rin." then he left.

UNSEEN=

Shiro stood in front of Rin's hospital room. A storm brewed in his mind. His son, his kind, feisty and stubborn son, is dying?

Shiro removed his glasses and covered his face with his hands. Tears streamed down his face but he wiped them away. 'It's no good to cry,' he thought, putting on his glasses. 'the doctor is right, I needs to be strong for Rin.'

And with the flame of determination on his eyes, he composed himself and entered the room.

Unseen=

Next chapter coming right up! - LittleFireOfLife


	2. Chapter 2

As Shiro entered the room, he immediately noticed the bed at the center of the room. Laying there is Rin, currently looking outside the window with disinterest. He look so small at the bed that is obviously too big for him. He's sickly pale, his skin a pasty white. He look flushed and fatigued.

 _'Be strong,'_ Shiro thought, clenching his fist. _'for Rin'_

"Hey, kiddo" Shiro whispered, catching Rin's attention.

"Tousan!" Rin beamed, but there is something different in his smile, like he's guilty and full of despair and he's trying to cover it up. Shiro didn't notice.

Shiro's heart dropped. That smile...how can he smile? Even when he's suffering...

Shiro forced a smile on his face. He inhaled sharply and sat on the chair beside the hospital bed.

"Rin..." Shiro gulped, "I have something to tell you."

"What is it, Tousan?" Rin tilted his head, his hair falling on his eyes.

Shiro grabbed Rin's hand and squeezed it comfortingly. Both for Rin and...himself.

"You...are very sick, Rin." Shiro trembled, "The-the doctor found an-an illness in your body."

"Does that mean, I need to take medicine?" Rin asked, eyebrows furrowing.

Shiro chuckled, blinking back tears.

"Yes, you need to take medicine." Shiro looked at Rin's innocent cerulean eyes. " That also means you can't get into fights anymore,"

"I'm serious, Rin" Shiro added when Rin opened his mouth to protest.

Rin closed his mouth for a moment but opened them again,

"But-but what about Yukio?! No one will protect him from bullies. And-and-"

Yukio's name struck Shiro like a cord. What about Yukio? He's already learning to use a gun to be an exorcist. And then now he will know that his brother have a terminal disease and probably only have eight to ten years to live?

He looked at Rin and whispered,

"We-we need to tell Yukio about this."

Rin's eyes widen in panic, "N-no! We can't-!"

"Rin!" Shiro exclaimed, grabbing Rin's shoulders, "We need to tell him. This is a serious matter. He's your brother, he have the right to know."

Rin looked away and mumbled,

"Fine."

UNSEEN=

As Yukio came home from training, he immediately noticed the lack of usual chattering and noise in the house. It's completely silent.

"Tousan? Niisan?" Yukio called, dread pooling at his stomach.

"In here Yukio,"

Shiro's voice came from the dining room. There is something in his voice that made Yukio nervous.

He walked toward the dining room and is greeted by the grim faces of his father and the clergymen, and a pale looking Rin. All of them are sitting while looking at him.

 _'Pale?'_ Yukio wondered, _'why does_ _Niisan look pale?'_

"Take a seat, Yukio. This is gonna be long conversation." Shiro spoke, is it just Yukio, or Shiro looks like he wants to cry?

"What's happening? Why is everyone so silent?" Yukio asked, sitting in front of Rin.

"Rin...collapsed this afternoon," Shiro's lips is pressed into a thin line, his eyes flashing.

Panic flashed in Yukio's eyes, "Collapsed? Niisan collapsed?"

"Yes," Shiro ran a hand through his hair. "The doctor said it-it's a terminal disease. The disease is unknown so they can't give Rin any treatments."

"The-the doctor also said that I-I only have eight to ten years to live right?" Rin's shaky voice echoed through the dining room, the expressions of the clergymen and Shiro obviously signals that Rin wasn't supposed to know that.

"H-how did you know that Rin? Did-did you eavesdrop on my conversation with the doctor?" the alarm in Shiro's voice didn't help Rin's guilty expression.

"I just want to know what's happening, I'm sorry." Rin apologized, looking down at his hands.

But Yukio paid it no mind. Yukio feels like the time stopped around him, the words 'eight to ten years to live' echoed repeatedly in his mind. _'Rin is dying?'_ Yukio stared at his brother's sickly pale face,

 _'His brother is dying?'_

Unseen=

To anyone who's wondering, yes,this is inspired by Freefall. - LittleFireOfLife


	3. Chapter 3

Yukio suddenly sat up from his seat, surprising everyone in the room. His hands were beside him, trembling. He stumbled into Rin and hugged him. He buried his face at the crook of Rin's neck.

"Why...why can't it be anyone else? Why you Niisan?" Yukio's voice cracks, Rin can feel the wetness of his shirt from Yukio's tears.

Rin smiled broken heartedly. He hugs Yukio back, tears running down his face. "I-it's okay, Yukio. Everything going to be al-alright."

Shiro closed his eyes. His children, God have mercy, his children. He walked towards them and embraced Rin and Yukio. His tears mixed with theirs. He never wants to let them go.

=UNSEEN=

The next few years was hell. One morning, Shiro woke up to find Yukio shaking him, telling him that Rin have a really high fever.

Shiro immediately rushes to Rin and Yukio's room. And found Rin sweating, his breathing ragged. He keeps coughing every few minutes. His sleeping face looks exhausted.

Shiro puts his hand on Rin's forehead, and quickly recoiled when he felt how hot it is.

"Get some medicine and a thermometer, Yukio." Shiro said. "Rin's definitely staying on bed today."

"O-okay," Yukio stuttered, rushing off to get the desired supplies.

Shiro gets a wet towel and puts it on Rin's forehead. He frowned,'This is bad, Rin's body is already weak, if he gets sick it will only aggraviate the disease.'

Yukio came back with the medicine and thermometer. He gave it to Shiro and sat down besides his twin. He looks worried while Shiro took Rin's temperature.

"Is Niisan going to be okay?" His eyebrows furrowed and his fingers twitched with worry.

Shiro clicked his tongue, the thermometer reads 103 F (A/N: 39.4 C). "He's going to be fine. He just needs some re-" Shiro was cut off by the sound of Rin coughing. He have woken up.

Rin continued to cough his lungs out. Mucus gargled at the back of his throat. Tears gathered at his blue eyes. He grabbed his throat. He can't breathe.

Shiro and Yukio immediately jumps into action. Shiro rubs Rin at the back and whispered comforting things at his ear, while Yukio pried Rin's hands from his own neck, not wanting Rin to hurt himself.

Rin started calming down and his coughings have subsided. Blood leaked out from his nose. Rin wiped the blood with the back of his hand. He looked at Yukio with pained half-lidded eyes.

"Yo-you should *cough* b-be at school." Rin sniffed, his fever-clouded brain made him forgot that it's Saturday.

Yukio smiled, worry clear in his teal eyes. "It's saturday Niisan. There's no school." He looked at Shiro, concern all over his face.

Shiro ran his hand through Rin's hair. "Sleep Rin, I'll wake you up later for lunch and your medicine."

And Rin did sleep. And when he woke up, Shiro and Yukio was there, taking turns at taking care of him.

=UNSEEN=

"Shouldn't Niisan's demon blood have protected him from the disease?"

Yukio's question made Shiro stop reading the reports for the attack at Nagasaki. Apparently a fox demon recked havoc at some market and some citizens are caught at the crossfire.

The question made Shiro frown, "I'm not really sure, but maybe it has something to do with the Kurikara being sealed."

"Then should we-"

Shiro cut off Yukio before he can finish, "We can't Yukio, if Rin ever draw the sword, there would be dire consiquences."

Yukio seems to have an inner battle with himself,

"Okay."

But in the end, the rational part of Yukio's brain won.

=UNSEEN=

They say that the best people seem to have the worst luck. And apparently, that's true.

Because for Yukio, his Niisan is one of the best people in the world. When he was a child, he always want to become like his older brother. Kind, brave, sincere and head strong. When he started training to become an exorcist, he can't help but be jealous on his brother. Rin can have all the free time he wants, while he needs to push himself on his training.

But when his brother was diagnosed, everything changed. Rin can no longer play outside without coughing up blood after. Rin can no longer run in a long period of time, cause it makes his lungs weaker. Rin can no longer protect Yukio from the bullies, because he became too frail to do so. Rin became restricted on so many things, that he can often be seen sad and solemn, looking outside the window. The only thing that he is allowed to do is cooking, and only because he begged Shiro to still let him cook. It made Yukio pity his brother. While he needs to train to become an exorcist, he's not restricted on doing things he enjoyed.

It made Yukio realize how unfair the world is.

Because while he trains how to use a gun to become an exorcist in the future, Rin is bed-ridden at the monastery, sick and looking out the window, hoping for a future that is non-existent.


	4. Chapter 4

I forgot the warnings and disclaimer at the previous chapters, sorry.

Warnings: Angst, swearing, violence and graphic illness.

Disclaimer: Sadly, I don't own Ao no Exorcist/Blue Exorcist.

Rin watched in shock as blue flames licked his skin.

Shock and glee flashed through the King of Rot's face.

"My Prince! I knew it was you! Those blue flames-! There is no mistake!" Astaroth grinned and grabbed Rin's wrist.

"Wha-!" Rin tried to pull away but the King of Rot have an iron grip.

"I'm taking you back to Gehenna. Satan will be so pleased that his son had come home!" The demon laughed, his sharp teeth showing.

"WHAT THE FUCK DO SATAN HAVE TO DO WITH THIS?! LET GO OF ME YOU BASTARD!" Rin screamed.

Astaroth kneeled in front of Rin, "I am Astaroth, the Demon King of Rot and Decay. I am going to take you back to Gehenna, my prince."

Footsteps caught the King of Rot and Rin's attention.

"Mischief is in their hearts,

Give them according to their deeds,"

Astaroth snarled, "Damned exorcist!"

"And according to the wickedness of their endeavors,

Give them after the work of their hands, render them to their desert.

Smite them and let them not rise again."

"I'll kill you! YOU EXORCIST!" The demon ran towards Shiro and tried to punch him, but Shiro grabbed Astaroth's wrist and judo flipped him.

"Blessed be the Lord.

The Lord is my strength, and my shield.

Thou shall perish!"

Shiratori screamed, thousands of coal tars escaping his mouth. His eyes rolled at the back of his head and he passed out.

Rin just watched in shock as Shiro exorcised Shiratori.

"D-dad?!" Rin yelled, "What just happened?!"

Shiro looked grim as he grabbed Rin and dragged him to the monastery, "There's no time Rin."

=UNSEEN=

As Shiro slammed the doors open, he immidiately started ordering the clergymen to lock the doors and windows. Shiro hurried and disappeared behind the podium and came back with a sword wrapped in red cloth. He gave it Rin.

"Old man! What the heck going on?! What happened to Shiratori earlier? And why are you giving me a sword?" Rin asked angrily.

Shiro grabbed Rin's shoulders and looked at him in the eyes.

"Rin...everyday I prayed this day will never come but I guess you can't avoid destiny." Shiro sighed, "That sword is called Kurikara, it's seals your flames and demonic heritage. And that thing that attacked you earlier is a demon."

"Eh? What?" Rin faked a laugh, "You're not making any sense Old man! There's no such thing as demons!"

"Rin!" Shiro yelled, his face clearly showing that he's not kidding. "I'm serious Rin. I'm not kidding or pranking you. That was a demon, and the reason why it want to take you to Gehenna," Shiro paused, "is because you're the son of Satan."

Rin stiffed. He tightened his hold at the Kurikara.

"Your abnormal strength, your uncontrolled temper, and those azure blue flames...you're the son of Satan, Rin."

Rin trembled. All this time...the people around him were right? He really is a demon?

"Bu-but what about Yukio? He-he's the son of Satan too." Rin choked out, his throat becoming uncomfortably tight.

"Yukio is one hundred percent human. You're the only one who inherited demonic traits."

Rin felt betrayed, he wanted to cry.

"Why didn't you tell me?" Rin pushed Shiro away, "Did Yukio know?"

Shiro didn't answer but his face showed it all. Rin closed his eyes tight.

Shiro tried to grab Rin but Rin flinched away.

"Were you secretly happy when you found out that I'm dying?" Rin whispered.

"No Rin-"

"DID YOU EVEN LOVED ME AT ALL?!"

SLAP!

Rin held his cheek, tearing up.

Shiro's eyes widen, "Rin! I'm so-"

Drops stained the floor.

"I hate you."

Time seem to stop for a moment .

Blue flames erupted around Shiro, his ears lengthened and teeth sharpening. He uttered some demonic language and a horrifying gate with twisted inscriptions appeared. Unknown dark sludge came out of it. Body parts littered the seemingly inescapable and disgusting sludge.

An insane laugh escaped Shiro's mouth as Rin stumbled back in horror.

"Well, well. Look who it is! It's my beloved son! It's been so long since I've seen you! You've grown!" Shiro-no this is not his Dad-Satan opened his arms and grinned.

"Come give your papa a hug!" Blood streamed down Shiro's face but that doesn't stop him from grabbing Rin's arm.

"I'm not your son, you bastard! Let me go!" Rin tried to pull back his arm but Satan seem to ignore him.

"It's time for you to come back home, son! It's an event to celebrate!" Satan grinned in triumph when they reached the gate. He threw Rin into the sludge.

"You bastard!" Rin said, but it came out as shaky and weak. He was slowly sinking into the dark sludge and body parts.

Suddenly the grin on Shiro's face faltered. The redness in Shiro's eyes suddenly disappeared.

"This...is my son! And I won't let you have him!" Shiro's voice resonates through Rin's very core. Shiro ripped his blade from his hip and aimed it at his stomach. Blood spurted out of the wound. The blue flames around him sputtered. Rin's eyes widen.

Rin gritted his teeth, his eyes full of determination. He grabbed Kurikara and removed the sword from the red cloth.

"I WON'T LET YOU DIE!"

Rin unsheathed the sword.

Blue flames erupted around Rin as he stabbed the gate. The blue flames engulfed the gate and blinded Rin, making him close his eyes. But he paid it no mind, because for the first time in his life, he felt good. Not feeling the fatigue and tiredness because of the goddamned disease.

As he sheathed Kurikara, the flames died down, only then did Rin open his eyes. The first image he saw was Shiro's bloodied body. Rin clenched his eyes shut. Tears fell from his eyes, one after another. Sobs echoed through the monastery.

Rin's chest seized up and he coughed up blood. Rin's eyes widen. Blood escaped from his nose.

"Shit..."

He collapsed besides Shiro's unmoving body, choking with his own blood. More blood splattered at the floor. His whole body trembled and shook. Tears continued to stream out of his eyes. It feels like every part of his body is being stabbed. His hand lets go of Kurikara.

He whimpered.

Why?

The disease...it's worse than before. Is it because he unsheathed the sword?

He can't think anymore. He tried clawing at the floor. He can't breathe.

The last thing he heard was Yukio's faint voice calling out his name.


	5. Announcement

Yo.

*sigh*

I don't really want to do this.

As you might have noticed, I haven't been updating. The reason for that is: 1. MAJOR writer's block and 2. Life is really coming down on me, hard. And let's just say, I'm really stressed right now. And since my health is poor, the stress is _nuh-uh._

So, this fic is on Hiatus at the moment.

I'll probably write some one-shots, two-shots here and there, but no really multi-chaptered ones...

But maybe, after all this shit has calmed down, I'll gonna pick this up again. I hope you guys understand.

And to all those people who reviewed, added this to their favorites, and just read it, thank you.

Peace,

LittleFireOfLife


	6. Chapter 5

_A/N: All I can say right now is sorryfor thelongwait. My health is extremely shitty and messed up these past few months (I find this freaking ironic that I'm writing a fic with the mc having extremely shitty health while, I, myself, have an extremely shitty health.). But...now here's chapter 5._

 _Warnings: Swearing, angst, probably OOCness, and again, graphic illness._

 _Disclaimer: I don't own Ao no Exorcist/Blue Exorcist._

[ **UNSEEN** ]

As Yukio sat beside Rin, staring at his brother's pale face. Rin's condition has worsened. Yukio clenched his jaw.

' _What happened back then, Rin?_ ' Yukio thought.

Tears threatened to fall from his eyes, he reached out to hold Rin's hand.

But he clenched his eyes shut and turned away.

"I promised to protect you, Nii-san..."

"But I'm sorry."

[ **UNSEEN** ]

The cold rain drenched Rin as he stands in front of the slab of cold stone, Kurikara strapped on his back. The cold will definitely make him sick later but he didn't care. All that matters is the name ingraved at the gravestone,

' _Fujimoto Shiro_ '

Shiro's dead.

The other people had already left. Saying their condolences then leaving. Rin doesn't know where Yukio is. Questions circled in his head.

Where is he? Is he okay?

' _He's probably blaming you for Shiro's death. It's all your fault. Afterall, you are Satan's son._ '

Rin clenched his fist and closed his eyes. No! It's not my fault! I'm not the Devil's son! I'm not-

 _I'm not a monster._

[ **UNSEEN** ]

Tap. Tap. Tap.

Rin turned to the sound of footsteps. Men dressed in black surrounded him. A man dressed in a ridiculous outfit also stood there, staring at Shiro's grave with an unreadable expression.

' _A clown?_ ' Rin thought.

"Hey! Who are you?" The clown's head turned at his direction and said,

"Ah, nice to meet you. I'm just visiting the old geezer,"

For a second, the clown's face returned to it's unreadable expression, but almost immediately vanished and was replaced by a toothy grin.

' _Toothy? Now that I noticed, his ears are pointed too. Is he a demon?_ ' Rin wondered.

"Now all those bothersome emotions gone, let's get down to business," Mephisto took off his hat and bowed, " I represent the Japanese branch of True Cross Knight Order. My name is Mephisto Pheles.

I was Father Fujimoto's friend. Please accept my condolences."

"Are you exorcists too?" Rin shifted into a defensive stance.

"Yes, indeed. And we know 'everything' about you." Mephisto took a step forward, "It seems that Father Fujimoto tried to raise you as human.

But contrary to his wishes, you still awakened."

Mephisto took another step forward, making Rin more anxious. He also noticed that the ever present fatigue also seems to increase because of the prolonged period of standing in the rain.

Rin shivered. Standing in the rain was definitely a bad idea.

"The Son of Satan wandering around Assiah is a threat to mankind. In the name of the Vatican, we are to dispose of you."

" What?" Rin stumbled back, not just from shock, but from also the sudden burning in his lungs. "You can't-!"

"You have two choices," Mephisto grinned, "Be killed by us,"

' _No way..._ ' Rin's gritted his teeth,

his hair hiding his eyes.

"Or kill us and run away." Mephisto tilted his head, " You can also kill yourself, so that's actually three choices."

"Now, choose one that would suit you best." Mephisto's eyes glinted.

"What if..."

Rin's voice made Mephisto pause.

"I'm already dying?"

[ **UNSEEN** ]

"What?" Mephisto was surprised to say the least. What does he mean that he's already dying?

Mephisto noticed that he seems to be trying to stop shivering.

"My body...is dying, it has been dying since I was eight. It has been slowly breaking down inside out. The doctor said that I was really lucky that I'm still alive after I turned 16, but it will be a miracle if I reach 18." Rin said bitterly.

"Make me one of you, even for a short amount of time! I'll show them! I'm - I'm the son of Fujimoto Shiro and no one else!"

Rin stayed silent for a brief moment to catch his breath, when suddenly his mouth twisted into a grimace.

Mephisto's interest skyrocketed when Rin suddenly coughed up blood.

This...is something he never ever would have predicted. Something so rare that he can barely contain the excitement of having a new...entertainment that will totally amuse him in the near future.

Mephisto laughed, "Amazing! Amazing! The Son of Satan's own body turning against him? The Son of Satan wanting to be an exorcist? Oh Satan damned, You humans are so amusing!"

Rin spit out the remaining blood in his mouth, "Shut up! I'll kick Satan's ass!"

"And how would you accomplish that with your own body dying?" Mephisto raised his eyebrow, mocking him.

This question made Rin pause. Honestly, he doesn't know the answer to Mephisto's question.

"I don't know." Rin's voice was quiet and weak, his spirit seemingly drained.

"Well then..."

"How about we make a deal?"

As Rin's face morphed into a confused expression, Mephisto laughed inwardly.

Very interesting, indeed.

[ **UNSEEN** ]

 _Sorry for the short and loopy chapter, I promise for a longer and better one next time. As for my health, I've been having therapies and taking my meds so I think I can manage. But for now, the chapters will come in a slower pace, so please have patience. That's all, chaossu._

 _Peace,_

 _LittleFireOfLife_


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